1. Field of the Invention
The present disclosure relates generally to a focusing ionization device and more particularly, to a focusing ionization device adapted to be applied in a mass spectrometer for gathering and ionizing gaseous analytes. The present disclosure further relates to a mass spectrometer using the focusing ionization device.
2. Description of the Related Art
Recently, the mass spectrometer using atmospheric pressure chemical ionization (hereinafter referred to as ‘APCI’) device has been widely used in the fields of identification of synthesized compounds, detection of environmental toxic substances, analysis of energy ingredients, development of drugs, biological metabolomics or pharmacometabolomics, analysis of natural products, food analysis, etc.
In general, a mass spectrometer includes an ionization device, a mass analyzer and a detector. FIG. 1 shows a schematic diagram of ionization mechanism of commercial APCI device 10. The conventional APCI device 10 includes a metal capillary 13 inserted through a high-temperature heater 11 and having an open end 131 that opens toward a sample inlet 21 of a mass analyzer 20. When the analyte solution 30 is sprayed from the open end 131 of the metal capillary 13, the analyte solution 30 is uniformly dispersed into droplets by a nebulization gas emitted in a coaxial direction of the metal capillary 13. The droplets are then heated by the high-temperature heater 11 and evaporate into gaseous analytes 30, which in turn are ionized to form single-charged analyte ions 31 by a corona discharge needle 50 connected to a high-voltage power supply and disposed adjacent to an outlet of the high-temperature heater 11 through gas phase ion-molecule reaction. Finally, analyte ions 31 travel into the mass analyzer 20 due to a potential difference established between the corona discharge needle 50 and the mass analyzer 20, a mass spectrum is thus obtained.
As shown in FIG. 1, because the plume-like analyte ions 31 may be obtained from the conventional APCI mechanism, that is, the analyte ions 31 may form a dispersion area much larger than a sectional area of the sample inlet 21 of the mass analyzer 20, at least 50% of the analyte ions 31 cannot flow into the mass analyzer 20. As a result, the mass spectrometer equipped with the conventional APCI device has the problems that the signal strength of analyte is significantly decreased and the detection limit cannot be lowered.
In order to improve the aforesaid problems, many methods for focusing ions to be transmitted into mass spectrometer by controlling electric field such as Field Asymmetric Ion Mobility Spectrometry (hereinafter referred to as ‘FAIMS’) have been developed. However, FAIMS has limited effect on ion-focusing under the influence of Maxwell's equation and has limited applicability due to its large volume and expensive price as well as it is not adapted to various mass spectrometers.